The present invention relates to a small firearm having a receiver for accommodating the system, and a valve which connects the interior of the receiver with the outside and which is designed in such a way that overpressure occurring in the receiver can be evacuated to the outside. There is always a risk in known firearms of the described type that explosive gases may gather in the receiver which may ignite when the firearm is fired. This risk exists in particular when the firearm, which may be an automatic or a semi-automatic weapon, belongs to the class using caseless ammunition where the entire mechanism of the firearm is enclosed in a case which takes the form of the stock and which is in the closed condition when the weapon is ready to fire. If the overpressure occurring when the explosive components ignite in the case is evacuated to the outside through a valve in order to prevent the case from being destroyed, there is the risk that damage may be caused by the hot gases escaping through the valve.
U.S. Pat. No. 2,814,972 describes a firearm with a closed receiver comprising a valve through which an overpressure arising inside the receiver can be evacuated to the outside. The flow path to be taken by the gas is designed as a labyrinth in which the gas is deflected several times and which guarantees that the flame of the burning gas will not emerge from the firearm. However, a labyrinth-like design of the flow path for the gas is very expensive and requires much space.
Further, it has been known from DE-C 25 44 995 to equip firearms having closed receivers with overpressure valves by means of which excessively high pressures occurring inside the firearm can be relieved. However, such relief valves are connected with the disadvantage that they are very sensitive to ingress of dirt, such as sand or the like, and that the cross-sectional surface available as gas outlet is relatively small. The receiver is dust-tight and water-tight, but not gas-tight. The rate of pressure rise inside the firearm is very high, in spite of such relief valves.